[PATCH bpf-next v3 3/7] bpf: create repeated fields for arrays.

[Kui-Feng Lee <thinker.li@gmail.com>]

The verifier uses field information for certain special types, such as
kptr, rbtree root, and list head. These types are treated
differently. However, we did not previously support these types in
arrays. This update examines arrays and duplicates field information the
same number of times as the length of the array if the element type is one
of the special types.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 kernel/bpf/btf.c | 81 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 76 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index d4c3342e2027..4a78cd28fab0 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3493,6 +3493,41 @@ static int btf_get_field_type(const char *name, u32 field_mask, u32 *seen_mask,
 
 #undef field_mask_test_name
 
+/* Repeat a field for a specified number of times.
+ *
+ * Copy and repeat a field for repeat_cnt
+ * times. The field is repeated by adding the offset of each field
+ * with
+ *   (i + 1) * elem_size
+ * where i is the repeat index and elem_size is the size of the element.
+ */
+static int btf_repeat_field(struct btf_field_info *info, u32 field,
+			    u32 repeat_cnt, u32 elem_size)
+{
+	u32 i;
+	u32 cur;
+
+	/* Ensure not repeating fields that should not be repeated. */
+	switch (info[field].type) {
+	case BPF_KPTR_UNREF:
+	case BPF_KPTR_REF:
+	case BPF_KPTR_PERCPU:
+	case BPF_LIST_HEAD:
+	case BPF_RB_ROOT:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	cur = field + 1;
+	for (i = 0; i < repeat_cnt; i++) {
+		memcpy(&info[cur], &info[field], sizeof(info[0]));
+		info[cur++].off += (i + 1) * elem_size;
+	}
+
+	return 0;
+}
+
 static int btf_find_struct_field(const struct btf *btf,
 				 const struct btf_type *t, u32 field_mask,
 				 struct btf_field_info *info, int info_cnt)
@@ -3505,6 +3540,19 @@ static int btf_find_struct_field(const struct btf *btf,
 	for_each_member(i, t, member) {
 		const struct btf_type *member_type = btf_type_by_id(btf,
 								    member->type);
+		const struct btf_array *array;
+		u32 j, nelems = 1;
+
+		/* Walk into array types to find the element type and the
+		 * number of elements in the (flattened) array.
+		 */
+		for (j = 0; j < MAX_RESOLVE_DEPTH && btf_type_is_array(member_type); j++) {
+			array = btf_array(member_type);
+			nelems *= array->nelems;
+			member_type = btf_type_by_id(btf, array->type);
+		}
+		if (nelems == 0)
+			continue;
 
 		field_type = btf_get_field_type(__btf_name_by_offset(btf, member_type->name_off),
 						field_mask, &seen_mask, &align, &sz);
@@ -3556,9 +3604,14 @@ static int btf_find_struct_field(const struct btf *btf,
 
 		if (ret == BTF_FIELD_IGNORE)
 			continue;
-		if (idx >= info_cnt)
+		if (idx + nelems > info_cnt)
 			return -E2BIG;
-		++idx;
+		if (nelems > 1) {
+			ret = btf_repeat_field(info, idx, nelems - 1, sz);
+			if (ret < 0)
+				return ret;
+		}
+		idx += nelems;
 	}
 	return idx;
 }
@@ -3575,6 +3628,19 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
 	for_each_vsi(i, t, vsi) {
 		const struct btf_type *var = btf_type_by_id(btf, vsi->type);
 		const struct btf_type *var_type = btf_type_by_id(btf, var->type);
+		const struct btf_array *array;
+		u32 j, nelems = 1;
+
+		/* Walk into array types to find the element type and the
+		 * number of elements in the (flattened) array.
+		 */
+		for (j = 0; j < MAX_RESOLVE_DEPTH && btf_type_is_array(var_type); j++) {
+			array = btf_array(var_type);
+			nelems *= array->nelems;
+			var_type = btf_type_by_id(btf, array->type);
+		}
+		if (nelems == 0)
+			continue;
 
 		field_type = btf_get_field_type(__btf_name_by_offset(btf, var_type->name_off),
 						field_mask, &seen_mask, &align, &sz);
@@ -3584,7 +3650,7 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
 			return field_type;
 
 		off = vsi->offset;
-		if (vsi->size != sz)
+		if (vsi->size != sz * nelems)
 			continue;
 		if (off % align)
 			continue;
@@ -3624,9 +3690,14 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
 
 		if (ret == BTF_FIELD_IGNORE)
 			continue;
-		if (idx >= info_cnt)
+		if (idx + nelems > info_cnt)
 			return -E2BIG;
-		++idx;
+		if (nelems > 1) {
+			ret = btf_repeat_field(info, idx, nelems - 1, sz);
+			if (ret < 0)
+				return ret;
+		}
+		idx += nelems;
 	}
 	return idx;
 }
-- 
2.34.1